A communication system provides for communication of information between a sending station and a receiving station. The sending and receiving stations are connected by way of a communication channel upon which the information is transmitted by the sending station to the receiving station. If necessary, the information is first converted into a form to permit its communication upon the communication channel.
Many types of communication systems have been developed, implemented, and regularly utilized. And, new types of communication systems have been, and continue to be, developed and implemented as a result of advancements in communication technologies.
A radio communication system is representative of a type of communication system that has benefited from advancements in communication technologies. A cellular communication system is an exemplary type of radio communication system. Cellular communication systems have been installed to encompass significant portions of the populated areas of the world and are popularly utilized to communicate telephonically therethrough. Typically, a user is permitted access to the cellular communication system through purchase of a service subscription to communicate therethrough. The user, sometimes referred to as a subscriber, typically utilizes a portable radio transceiver, referred to as a mobile station, to effectuate communications by way of the cellular communication system. Mobile stations are typically constructed to mimic the operation of a conventional, wireline, telephonic station, providing full-duplex communications.
Successive generations of cellular communication systems have been developed and implemented. As advancements have permitted, improvements to existing systems have been implemented, and subsequent-generation systems have been installed.
First-generation cellular communication systems generally utilize analog communication schemes while subsequent-generation, communication systems generally utilize digital communication schemes. Second-generation cellular communication systems utilize various types of, generally, fixed-rate digital communication schemes. Examples of second-generation systems includes a GSM (General System for Mobile Communications) system and an IS-95. And, third-generation cellular communication systems also utilize digital communication techniques while further providing for multiple data rate communications. GSM/EDGE (GSM/Enhanced Data or GSM Evolution) and W-CDMA (Wide Band-CDMA) communication systems are exemplary of third-generation cellular communication systems.
Full-duplex communications are provided through the allocation of separate communication channels upon which to send information and to receive information, respectively. In at least several of the cellular communication systems, and of interest herein, are communication channels defined through the use of frequency division techniques. That is, the separate communication channels utilized to effectuate full-duplex communications are offset from one another in frequency within separate frequency bands.
Mobile stations constructed for use in such types of systems sometimes utilize duplexer filters. Duplexer filters used in such mobile stations are typically connected to the antenna transducer of the mobile station and include separate pass bands corresponding to the frequency bands at which the separate communication channels are defined. That is, the duplexer filter includes a receive portion of a first pass band centered about a first center frequency and a transmit filter portion having a second pass band centered about a second center frequency. The first and second pass bands are selected to correspond to the ranges that are defined in the communication system in which the mobile station is to be operable and are generally of non-overlapping frequencies.
A filter duplexer must exhibit high levels of rejection between the separate pass bands so that required linearity conditions are maintained. For instance, the duplexer filter must also be of band-reject characteristics such that a send signal, originated at the mobile station is not passed through the receive portion of the mobile station to be operated thereon, together with the intended receive signal.
At least one existing, cellular communication standard separates the frequency bands of the frequency-band set by a 20 MHz guard band.
Due to the popularity of usage of cellular communication systems to communicate therethrough, proposals have been set forth to allocate additional portions of the electromagnetic spectrum for cellular communications. For instance, portions of the 2.5 and 2.7 GHz frequency band are proposed to be 5 MHz extensions of the 1.9 GHz PCS band are proposed to be allocated for cellular communication. The 5 MHz extension would reduce the size of the guard band separating the bands of the frequency-band set. Such reduction necessitates corresponding change in the duplexer characteristics.
A mobile station operable in a cellular communication system implemented at the extended frequency bands needs to have a duplexer having split-band characteristics to permit appropriate operation of the mobile station at such frequency bands. And, because mobile stations are also constructed to be of increasingly miniaturized dimensions, size constraints prevent the increase in the dimensions of the duplexers.
A duplexer, capable of split-band operation at disparate frequency bands requiring minimal, or no, guard bands separating the frequency bands, that exhibits high levels of rejection, and is of small physical dimensions would therefore be advantageous.
It is in light of this background information related to filter duplexers that the significant improvements of the present invention have evolved.